This invention relates to a universal combustion system for thermal devices, in particular for positive-displacement, thermal engines where use of different kinds of fuel is advantageous, and in particular, where high compression ratios or supercharging make existing systems inefficient or inoperative. The universal combustion system of this invention is an improvement over the system described in our patent, "Multi-Fuel Precombustor Unit", U.S. Pat. No. 5,224,450, issued Jul. 6, 1993, and incorporated herein by reference. The universal combustion system utilizes certain features for automatic actuation in conjunction with the engine cycle in co-pending application, Ser. No. 08/613,839 filed Mar. 11, 1996, entitled, "Self Injection System."
The universal combustion system is designed to permit advances in engine efficiency through high compression ratios and clean burning of fuels to be extended to fuels of lower quality or of different type, such as natural gas. As a result of increasingly stringent air quality regulations related to the products of combustion from internal combustion engines, new fuel formulations are being required for vehicles in the industrialized countries. Not only do the new fuel formulations add significantly to the cost of fuel, such formulations are not available in most other parts of the world. The inability of spark ignited engines to adapt to low quality fuels without substantial loss in power and performance has created a great economic burden for the world population. Additionally, the migration toward more sophisticated gasoline formulations to ensure clean burning in modern high-performance engines, has limited the fuel products available from existing oil reserves and restricted the competitiveness of alternative fuels such as alcohol and natural gas.
Ordinarily, the methane, octane and cetane numbers affect the type of fuel that can be burned in an internal combustion engine without inefficient combustion. In modern spark ignited engines burning gasoline, the increased pressure ratio and elimination of the anti-knock compound, tetraethyllead, has required the addition of more expensive exotic additives to achieve the octane rating necessary to prevent detonation.
Similarly, cetane fuels such as jet fuel (kerosene) and diesel fuel (gas oil) are not efficiently combusted in spark-ignited engines designed for lighter gasoline fractions.
Finally, for gaseous fuel such as methane, or natural gas, the displacement of air by the gaseous fuel in the charging cycle greatly reduces the generated thermal energy and efficiency of the engine. Supplemental compression to compensate for performance loss will frequently result in premature detonation.
Similar limitations are associated with the admission of air and gasoline mixtures into the cylinder via a carborator, or by fuel injection into the intake port, or in any situation where autoignition prior to the timing of the controlled ignition may result.
Because of the variations in fuel characteristics, engines designed for one type of fuel cannot utilize another type without extensive modification in the physical structure of the fuel delivery system and engine.
It is a primary object of this invention to resolve the problems in switching fuel by a system that may be regulated, preferably by an electronic control system, to operate with a variety of different fuels. With the universal combustion system of this invention, the most cost competitive fuel or the locally available fuel can be used. Since the system compensates for the characteristics of the fuel, regardless of octane and cetane number, then a variety of fuels, including common oil derived fuels, alcohols, and combustible gases can be used. In addition to convenience, great savings in cost can be effected by the use of cheaper fuels and the lower prices that result in the competition from a variety of different useable fuels.